Calibration method and calibration apparatus for calibrating mismatch between i-path and q-path of transmitter/receiver

ABSTRACT

A method for calibrating mismatches of an in-phase signal path and a quadrature signal path of a transmitter, including: additionally configuration at least one mixer calibration coefficient at a transmitting part of the transmitter; obtaining at least one mixer testing signal from the transmitting part via loopback for spectrum analysis to derive at least one mixer spectrum analysis result; adjusting the mixer calibration coefficient of the transmitting part according to the mixer spectrum analysis result; and additionally utilizing an in-phase signal path finite impulse response filter and a quadrature signal path finite impulse response filter to calibrate mismatches between a low pass filter of the in-phase signal path of the transmitting part of the transmitter and a low pass filter of the quadrature signal path of the transmitting part of the transmitter. A similar mismatch calibration operation may be applied to a receiver.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosed embodiments of the present invention relate to acalibration method, and more particularly, to a systematic defectanalysis method which is able to calibrate mismatches between anin-phase signal path and a quadrature-phase signal path of atransmitter/receiver, and an associated apparatus.

2. Description of the Prior Art

A modulation technique which is defined as ‘complicated’ carries moreinformation than in general cases. The data transmission rate may beincreased through sophisticated modulation processes, e.g. 64-QuadratureAmplitude Modulation (QAM) or 256-QAM. A need for high level QAM istherefore increasing. To improve the transmission and receiving abilityof the high level QAM, an Error Vector Magnitude (EVM) of acommunication system has to be correspondingly improved. One factoraffecting the EVM is the extent of an imbalance between in-phase andquadrature-phase (IQ imbalance). The main factor which induces IQimbalance is a mismatch between the in-phase path and thequadrature-phase path of a radio frequency (RF) circuit. Even a slightdeviation may result in an imperfect quadrature modulation/demodulationprocess and affect the overall communication system, which leads to ahigh reception bit error rate (BER). The deviation is divided into twocategories: amplitude deviation and phase deviation, wherein bothcategories can introduce an image signal at symmetric frequency. FIG. 1is a diagram illustrating a received signal at a receiving terminal andan introduced image signal of the received signal. The differencebetween the magnitude of the received signal and the magnitude of theimage signal is known as the image rejection ratio (IRR). In practice,the IRR is inversely proportional to the extent of the IQ imbalance.

In order to solve the above issue, a calibration process (i.e. IQcalibration) may be performed upon a transceiver before the transceiverstarts to transmit and receive data. The IQ mismatch phenomenon canpresent itself in two ways. A first way is, when sending carriers to amixer of an in-phase path and a quadrature-phase path from a localoscillator (LO), it is difficult to keep a perfect phase difference of90 degrees, or to guarantee that two amplitudes of the two signals areexactly the same. The other way is imperfection of the circuitmanufacturing process, which causes component mismatches between the twopaths, such as mismatches between a low-pass filter (LPF) pair, ananalog-to-digital converter (ADC) pair, a digital-to-analog converter(DAC) or a gain amplifier pair. The component mismatches can alsoexplain the interfering image signal as shown in FIG. 1 and arefrequency dependent resulting in the extent of interference by imagesignals at different frequencies varying.

In summary, how to perform IQ calibration in a communication system hasbecome an urgent issue in the field.

SUMMARY OF THE INVENTION

According to the disclosed embodiments of the present invention,systematic defect analysis methods which are able to calibratemismatches between an in-phase signal path and a quadrature signal pathof a transmitter or a receiver are disclosed to improve theaforementioned issues. An associated apparatus is also disclosed.

According to an exemplary embodiment of the present invention, a methodfor calibrating mismatches between a first signal path and a secondsignal path of a transmitter is disclosed, wherein one of the firstsignal path and the second signal path is an in-phase signal path; andthe other is a quadrature signal path. The calibration method comprises:additionally configuring at least one mixer calibration coefficient at atransmission terminal of the transmitter; producing a first transmissionsignal according to at least one mixer test signal and the mixercalibration coefficient, and looping back the first transmission signalfor spectrum analysis to derive at least one mixer spectrum analysisresult; adjusting the mixer calibration coefficient according to themixer spectrum analysis result to derive a final value of the mixercalibration coefficient for calibrating a mismatch between a first mixerof the first signal path and a second mixer of the second signal path;and performing a first signal path finite impulse response (FIR)filtering process upon the first signal path by additionally utilizing afirst signal path FIR filter, and performing a second signal path FIRfiltering process upon the second signal path by additionally utilizinga second signal path FIR filter, to calibrate a mismatch between a firstfilter of the first signal path and a second filter of the second signalpath.

According to another exemplary embodiment of the present invention, amethod for calibrating mismatches between a first signal path and asecond signal path of a receiver is disclosed, wherein one of the firstsignal path and the second signal path is an in-phase signal path; andthe other is a quadrature signal path. The calibration method comprises:additionally configuring at least one mixer calibration coefficient at areceiving terminal of the receiver; outputting the mixer test signal ata transmission terminal of the receiver as a first transmission signal,and looping back the first transmission signal and performing spectrumanalysis upon the received first transmission signal after it passesthrough the mixer calibration coefficient, for deriving at least onemixer spectrum analysis result; adjusting the mixer calibrationcoefficient of the receiver according to the mixer spectrum analysisresult to derive a final value of the mixer calibration coefficient forcalibrating a mismatch between a first mixer of the first signal pathand a second mixer of the second signal path; and performing a firstsignal path finite impulse response (FIR) filtering process upon thefirst signal path by additionally utilizing a first signal path FIRfilter, and performing a second signal path FIR filtering process uponthe second signal path by additionally utilizing a second signal pathFIR filter, to calibrate a mismatch between a first filter of the firstsignal path and a second filter of the second signal path.

According to yet another exemplary embodiment of the present invention,an apparatus for calibrating mismatches between a first signal path anda second signal path of a transmitter is disclosed, wherein one of thefirst signal path and the second signal path is an in-phase signal path;and the other is a quadrature signal path. The calibration apparatuscomprises a mixer calibration coefficient unit, a mixer test signalgenerating unit, a spectrum analysis unit, a mixer calibrationcoefficient adjustment unit and a finite impulse response (FIR)filtering unit. The mixer calibration coefficient unit is coupled to atransmission terminal of the transmitter, wherein the mixer calibrationcoefficient unit is configured to have at least one mixer calibrationcoefficient. The mixer test signal generating unit is arranged forproducing a first transmission signal by controlling at least one mixertest signal to start from the transmission terminal and to pass throughthe mixer calibration coefficient. The spectrum analysis unit isarranged for performing spectrum analysis upon the received firsttransmission signal to derive at least one mixer spectrum analysisresult. The mixer calibration coefficient adjustment unit is arrangedfor adjusting the mixer calibration coefficient according to the mixerspectrum analysis result to derive a final value of the mixercalibration coefficient for calibrating a mismatch between a first mixerof the first signal path and a second mixer of the second signal path.The finite impulse response (FIR) filtering unit is coupled to thetransmission terminal of the transmitter, and arranged for performing afirst signal path FIR filtering process upon the first signal path byadditionally utilizing a first signal path FIR filter, and performing asecond signal path FIR filtering process upon the second signal path byadditionally utilizing a second signal path FIR filter, to calibrate amismatch between a first filter of the first signal path and a secondfilter of the second signal path.

According to yet another exemplary embodiment of the present invention,an apparatus for calibrating mismatches between a first signal path anda second signal path of a receiver is disclosed, wherein one of thefirst signal path and the second signal path is an in-phase signal path;and the other is a quadrature signal path. The calibration apparatuscomprises: a mixer calibration coefficient unit, a mixer test signalgenerating unit, a spectrum analysis unit, a mixer calibrationcoefficient adjustment unit and a finite impulse response (FIR)filtering unit. The mixer calibration coefficient unit is coupled to areceiving terminal of the receiver, wherein the mixer calibrationcoefficient unit is configured to have at least one mixer calibrationcoefficient. The mixer test signal generating unit is arranged foroutputting the mixer test signal at a transmission terminal of thereceiver as a first transmission signal. The spectrum analysis unit isarranged for performing spectrum analysis upon the received firsttransmission signal which passes through the mixer calibrationcoefficient, to derive at least one mixer spectrum analysis result. Themixer calibration coefficient adjustment unit is arranged for adjustingthe mixer calibration coefficient according to the mixer spectrumanalysis result to derive a final value of the mixer calibrationcoefficient for calibrating a mismatch between a first mixer of thefirst signal path and a second mixer of the second signal path. Thefinite impulse response (FIR) filtering unit is coupled to the receivingterminal of the receiver, and arranged for performing a first signalpath FIR filtering process upon the first signal path by additionallyutilizing a first signal path FIR filter, and performing a second signalpath FIR filtering process upon the second signal path by additionallyutilizing a second signal path FIR filter, to calibrate a mismatchbetween a first filter of the first signal path and a second filter ofthe second signal path.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a received signal at a receivingterminal and an introduced image signal of the received signal.

FIG. 2 is a diagram illustrating a transmitter of a transmitter of adirect-conversion transceiver.

FIG. 3 is a diagram illustrating a receiver of a direct-conversiontransceiver.

FIG. 4 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to an embodiment of the presentinvention.

FIG. 5 is a diagram illustrating the calibration apparatus of FIG. 4 inanother configuration.

FIG. 6 is a diagram illustrating the first I-path frequency responsecomputing unit according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating the first I-path frequency responsecomputing unit according to another embodiment of the present invention.

FIG. 8 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to another embodiment of the presentinvention.

FIG. 9 is a diagram illustrating the calibration apparatus of FIG. 8 inanother configuration.

FIG. 10 is a diagram illustrating the second I-path frequency responsecomputing unit according to an embodiment of the present invention.

FIG. 11 is a diagram illustrating the second I-path frequency responsecomputing unit according to another embodiment of the present invention.

FIG. 12 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to an embodiment of the presentinvention.

FIG. 13 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to another embodiment of the presentinvention.

FIG. 14 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to another embodiment of the presentinvention.

FIG. 16 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention.

FIG. 17 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention.

DETAILED DESCRIPTION

Certain terms are used throughout the description and following claimsto refer to particular components. As one skilled in the art willappreciate, manufacturers may refer to a component by different names.This document does not intend to distinguish between components thatdiffer in name but not function. In the following description and in theclaims, the terms “include” and “comprise” are used in an open-endedfashion, and thus should be interpreted to mean “include, but notlimited to . . . ”. Also, the term “coupled” is intended to mean eitheran indirect or direct electrical connection. Accordingly, if one deviceis coupled to another device, that connection may be through a directelectrical connection, or through an indirect electrical connection viaother devices and connections.

Regarding the concept of a disclosed calibration apparatus of thepresent invention, a mathematic aspect is initially discussed. FIG. 2 isa diagram illustrating a transmitter 200 of a direct-conversiontransceiver. To test whether mismatches exist between an in-phase signalpath (I-path) 202 and a quadrature signal path (Q-path) 204, asingle-tone signal (i.e. a signal which only consists of a singlefrequency component) may be utilized as a test signal to pass throughthe signal paths of the transmitter 200; and then the signal outputtedfrom the transmitter 200 is inspected to identify if there is an imagesignal. A strong image signal indicates that the I-path 202 and theQ-path 204 are highly mismatched. The transmitter 200 includes acalibration coefficient unit 206 which has two calibration coefficients:a first coefficient X and a second coefficient Y. As shown in FIG. 2,the first coefficient X is utilized to calibrate amplitude mismatchesbetween the I-path 202 and the Q-path 204; and the second coefficient Yis utilized to calibrate phase mismatches between the I-path 202 and theQ-path 204. The image signal can be completely canceled or mitigated byoptimizing the first coefficient X and the second coefficient Y of thecalibration coefficient unit 206. Theoretically, to completelycompensate the effect of the image signal, the following equations'conditions have to be met.

$\begin{matrix}{X = \frac{1}{R\; {\cos (\Phi)}}} & (1) \\{Y = {- {\tan (\Phi)}}} & (2)\end{matrix}$

where Φ denotes a phase difference produced by a single-tone test signalwith frequency f_(s) which passes through the I-path 202 and the Q-path204, respectively; R denotes an amplitude ratio produced by thesingle-tone test signal with frequency f_(s) which passes through theI-path 202 and the Q-path 204, respectively.

FIG. 3 is a diagram illustrating a receiver 300 of a direct-conversiontransceiver. To test whether mismatches exist between an in-phase signalpath (I-path) 302 and a quadrature signal path (Q-path) 304, asingle-tone signal (i.e. a signal only consisting of a single frequencycomponent) may be utilized as a test signal to pass through the signalpaths of the receiver 300; and then the signal outputted from thereceiver 300 is inspected to identify if there is an image signal. Thereceiver 300 includes a calibration coefficient unit 306 which has twocalibration coefficients: a first coefficient X and a second coefficientY. As above, when conditions of equation (1) and equation (2) are bothmet, the image signal can be completely canceled. Φ denotes a phasedifference produced by a single-tone test signal with frequency f_(s)which passes through the I-path 302 and the Q-path 304, respectively; Rdenotes an amplitude ratio produced by the single-tone test signal withfrequency f_(s) which passes through the I-path 302 and the Q-path 304,respectively.

Detailed descriptions associated with the disclosed apparatus are givenin the following paragraphs. FIG. 4 is a diagram illustrating acalibration apparatus applied for calibrating mismatches between a firstsignal path and a second signal path of a transmitter according to anembodiment of the present invention; wherein one of the first signalpath and the second signal path is an I-path and the other is a Q-path.The transmitter 400 includes at least one portion (e.g. a portion orall) of an electronic device, wherein the electronic device includes atleast a transmission circuit and a receiving circuit. For example, thetransmitter 400 may comprise a portion of an electronic device, and moreparticularly, the electronic device includes at least a transmissioncircuit and at least a receiving circuit. In another example, thetransmitter 400 can be the whole of the electronic device mentionedabove. Examples of the electronic device may include, but are notlimited to, a mobile phone (e.g. a multifunctional mobile phone), amobile computer (e.g. tablet computer), a personal digital assistant(PDA), and a personal computer such as a laptop computer. For example,the transmitter 400 may be a processing module of the electronic device,such as a processor. In another example, the transmitter 400 may be theentire electronic device; however, this is for illustrative purposes,and not a limitation of the present invention. In practice, anyalternative design which can achieve the same or similar functions fallswithin the scope of the present invention. According to an alternativedesign of the present invention, the transmitter 400 is a system of theelectronic device, and the electronic device is a sub-system of thesystem. More particularly, the electronic device may include an OFDMcircuit, wherein the transmitter 400 is able to calibrate the OFDMcircuit, although this is not a limitation of the present invention.

As shown in FIG. 4, the transmitter 400 includes a mixer test signalgenerating unit 402, a low-pass filter test signal generating unit 404,a mixer calibration coefficient unit 406, a switching unit 408, alow-pass filter calibration coefficient unit 410, a tap coefficientcomputing unit 412, a finite impulse response (FIR) filtering unit 414,a first digital-to-analog converter (DAC) 416, a second DAC 418, a firstlow-pass filter 420, a second low-pass filter 422, a first mixer 424, asecond mixer 426, an oscillator 428, a power amplifier 430, a receivingterminal 432, a spectrum analysis unit 434, a mixer calibrationcoefficient adjustment unit 436 and a low-pass filter calibrationcoefficient adjustment unit 438. According to the disclosed embodiment,each time after the transmitter 400 is activated (e.g. the transmitter400 is powered on or reset) and before a normal data transmissionstarts, in order to improve mismatches of circuit characteristicsbetween an I-path (i.e. the path along with the first DAC 416, the firstlow-pass filter 420 and the first mixer 424) and a Q-path (i.e. the pathalong with the second DAC 418, the second low-pass filter 422 and thesecond mixer 426) of a transmission terminal 440 (including at least thefirst DAC 416, the second DAC 418, the first low-pass filter 420, thesecond low-pass filter 422, the first mixer 424, the second mixer 426,and the oscillator 428) of the transmitter 400, the transmitter 400enters into a calibration parameters computing mode. To be morespecific, at the calibration parameters computing mode, calibrationparameters can be optimized through a computing process with respect tothe difference between the I-path and the Q-path of the transmissionterminal 440 of the transmitter 400; After that, the transmissionterminal 440 is allowed to enter a normal data transmission mode totransmit data by employing the additional calibration parameters derivedin the above steps. This is for illustrative purposes, not a limitationof the present invention. For example, the first low-pass filter 420 andthe second low-pass filter 422 of the transmitter 400 may be filters ofanother type.

Specifically, the first point of the calibration process of thedisclosed embodiment is to add the mixer calibration coefficient unit406 into the transmission terminal 440 of the transmitter 400, whereinthe mixer calibration coefficient unit 406 may be directly or indirectlycoupled to the transmission terminal 440 of the transmitter 400, and themixer calibration coefficient unit 406 possesses a first mixercalibration coefficient X and a second mixer calibration coefficient Y.The first mixer calibration coefficient X is placed on the I-path of thetransmission terminal 440 of the transmitter 400, which means that thesignal passing through the I-path of the transmission terminal 440 ismultiplied by the first mixer calibration coefficient X, so that theamplitude mismatch between the I-path signal and the Q-path signalinduced by mixer mismatches between the I-path and the Q-path of thetransmitter 440 can be calibrated. The second mixer calibrationcoefficient Y is placed between the I-path and the Q-path of thetransmission terminal 440 of the transmitter 400, which means that thesignal passing through the I-path of the transmission terminal 440 ismultiplied by the second mixer calibration coefficient Y first, and thenadded to the signal passing through the Q-path of the transmissionterminal 440, so that the phase mismatch between the I-path signal andthe Q-path signal induced by mixer mismatches between the I-path and theQ-path of the transmitter 440 can be calibrated. This is forillustrative purposes, and not a limitation of the present invention.For example, more than two calibration coefficients may be employed, andits complexity and accuracy may also change accordingly. The first mixercalibration coefficient X and the second mixer calibration coefficient Ymay be configured in an opposite manner (i.e. the first mixercalibration coefficient X set on the Q-path, the second mixercalibration coefficient Y set between the I-path and the Q-path, and theadder set on the I-path). Please note that, in this embodiment, aninitial value of the first mixer calibration coefficient X may be set to1, and an initial value of the second mixer calibration coefficient Ymaybe set to 0 as a result of the first mixer calibration coefficient Xbeing equal to 1 and the second mixer calibration coefficient Y beingequal to 0 in an ideal case without mixer mismatches. Deductionsassociated with how to derive the optimal value of the first mixercalibration coefficient X and the second mixer calibration coefficient Yare provided in the following paragraphs.

Specifically, the second point of the calibration process of thedisclosed embodiment is adding the FIR filtering unit 414 into thetransmission terminal 440 of the transmitter 400, wherein the FIRfiltering unit 414 may be directly or indirectly coupled to thetransmission terminal 440 of the transmitter 400, and the FIR filteringunit 414 possesses a first FIR filter 4142 and a second FIR filter 4144.The first FIR filter 4142 is used for an FIR filtering process withrespect to the I-path of the transmission terminal 440; and the secondFIR filter 4144 is used for an FIR filtering process with respect to theQ-path of the transmission terminal 440. Through appropriate design tapcoefficients of the first FIR filter 4142 and the second FIR filter4144, respectively, mismatches between the first low-pass filter 420 andthe first DAC 416 of the I-path signal and the second low-pass filter422 and the second DAC 418 of the Q-path signal of the transmissionterminal 440 of the transmitter 400 can be solved. Please note that, inthis embodiment, the tap coefficients of the first FIR filter 4142 andthe second FIR filter 4144 may be configured to an initial value, tokeep the signal passing through the first FIR filter 4142 and the secondFIR filter 4144 untouched. In an ideal case, the tap coefficients of thefirst FIR filter 4142 and the second FIR filter 4144 should maintaintheir initial value. Deductions associated with how to derive theoptimal value of the tap coefficients of the first FIR filter 4142 andthe second FIR filter 4144 are provided in the following paragraphs.

In this embodiment, the mismatches aimed to be eliminated at thecalibration parameters computing mode are the mismatch between the firstmixer 424 and the second mixer 426, the mismatch between the firstlow-pass filter 420 and the second low-pass filter 422, and the mismatchbetween the first DAC 416 and the second DAC 418. The computation of themismatch between the first mixer 424 and the second mixer 426 is muchsimpler because the first mixer 424 and the second mixer 426 operate ata fixed frequency, i.e. a local oscillator frequency f_(osc) of theoscillator 428. In contrast, the computation of the mismatch between thefirst low-pass filter 420 and the second low-pass filter 422 and thecomputation of the mismatch between the first DAC 416 and the second DAC418 is complex because they process transmission signal with widebandwidth suffering from frequency-dependent mismatch. According to thisembodiment, it is preferable to derive the first mixer calibrationcoefficient X and the second mixer calibration coefficient Y of themixer calibration coefficient unit 406 first, and then to deal with theFIR filtering unit 414 based on the above basis. Before working on themixer calibration coefficient unit 406, the mixer calibrationcoefficient unit 406 should be reset, and in addition, the tapcoefficients of the first FIR filter 4142 and the second FIR filter 4144of the FIR filtering unit 414 should also be reset, which avoids thecharacteristics of signal passing through the FIR filtering unit 414being altered. In addition, the low-pass filter calibration coefficientunit 410 is utilized as an auxiliary tool to derive the tap coefficientsof the first FIR filter 4142 and the second FIR filter 4144 of the FIRfiltering unit 414. In other words, the low-pass filter calibrationcoefficient unit 410 is temporarily needed only when computing the tapcoefficients of the FIR filtering unit 414, hence the switching 408 isconfigured to bypass the low-pass filter calibration coefficient unit410 when the transmitter 400 is working on deriving the mixercalibration coefficient unit 406 or the normal data transmission andreception mode, as shown in FIG. 4. The present invention is not limitedto the above mentioned configurations, however. For instance, whenderiving the first mixer calibration coefficient X and the second mixercalibration coefficient Y of the mixer calibration coefficient unit 406,it is also feasible to bypass the FIR filtering unit 414, so that thefirst mixer calibration coefficient X and the second mixer calibrationcoefficient Y of the mixer calibration coefficient unit 406 cannot beaffected by the FIR filtering unit 414.

Next, the mixer test signal generating unit 402 generates a first mixercalibration test signal TS1 and a second mixer calibration test signalTS2, wherein the first mixer calibration test signal TS1 is a singletone signal having a first mixer calibration test frequency formed byadding a frequency f_(osc) of a local oscillator 428 of the transmitter440 with a specific frequency f₀; similarly, the second mixercalibration test signal TS2 is a single tone signal having a secondmixer calibration test frequency formed by subtracting a specificfrequency f₀ from the frequency f_(osc) of a local oscillator 428 of thetransmitter 440. The first mixer calibration test signal TS1 passesthrough the mixer calibration coefficient unit 406 and bypasses thelow-pass filter calibration coefficient unit 410 via the switching unit408, and then goes through the FIR filtering unit 414 with the initialsetting and the transmission terminal 440, and then loops back to thereceiving terminal 432. A spectrum analysis is then performed upon thereceived signal by the spectrum analysis unit 434 to obtain a mixerspectrum analysis result. The mixer spectrum analysis result at leastindicates information associated with an image signal corresponding tothe first mixer calibration test signal TS1. Accordingly, the mixercalibration coefficient adjustment unit 436 can adjust the first mixercalibration coefficient X to reduce the image signal of the first mixercalibration test signal TS1 toward a relative minimum value. Thecorresponding first mixer calibration coefficient X is preserved as afirst result X_(a); and then the mixer calibration coefficientadjustment unit 436 can adjust the second mixer calibration coefficientY to reduce the image signal of the first mixer calibration test signalTS1 toward a relative minimum value. The corresponding second mixercalibration coefficient Y is preserved as a second result Y_(a). Thedetails of the adjustment of the first mixer calibration coefficient Xand the second mixer calibration coefficient Y may be designed accordingto practical considerations, such as accuracy and cost requirements. Forexample, a specific step size can be utilized as a unit of adjustment.

The second mixer calibration test signal TS2 also passes through themixer calibration coefficient unit 406 and bypasses the low-pass filtercalibration coefficient unit 410 by the switching unit 408, and thenpasses through the FIR filtering unit 414 with the initial setting andthe transmission terminal 440, and loops back to the receiving terminal432. A spectrum analysis is performed upon the received signal by thespectrum analysis unit 434 to obtain a mixer spectrum analysis result.The mixer spectrum analysis result at least indicates informationassociated with an image signal of the second mixer calibration testsignal TS2. Accordingly, the mixer calibration coefficient adjustmentunit 436 can adjust the first mixer calibration coefficient X to reducethe image signal of the second mixer calibration test signal TS2 towarda relative minimum value. The corresponding first mixer calibrationcoefficient X is preserved as a third result X_(b); the mixercalibration coefficient adjustment unit 436 can then adjust the secondmixer calibration coefficient Y to reduce the image signal of the secondmixer calibration test signal TS2 toward a relative minimum value. Thecorresponding second mixer calibration coefficient Y is preserved as afourth result Y_(b). Lastly, the final value of the first mixercalibration coefficient X can be obtained by averaging the first resultX_(a) and the third result X_(b); and the final value of the secondmixer calibration coefficient Y can be obtained by averaging the secondresult Y_(a) and the fourth result Y_(b). It should be noted that thederived first mixer calibration coefficient X and the second mixercalibration coefficient Y here are approximated values rather than idealvalues, i.e. the approximated values come from averaging the calibrationresults of the first mixer calibration test frequency (f_(osc)+f₀) andthe second mixer calibration test frequency (f_(osc)˜f₀).

Next, the mismatch between the first low-pass filter 420 and the secondlow-pass filter 422 are dealt with at the calibration parameterscomputing mode in the subsequent step. As mentioned above, the first FIRfilter 4142 coupled to the I-path of the transmission terminal 440 isutilized to perform the I-path FIR filtering process upon the I-path;and the second FIR filter 4144 coupled to the Q-path of the transmissionterminal 440 is utilized to perform the Q-path FIR filtering processupon the Q-path, to calibrate the mismatch between the first low-passfilter 420 and the second low-pass filter 422 and the mismatch betweenthe first DAC 416 and the second DAC 418. The main purpose is tocompensate the mismatches between the I-path and the Q-path, which meansthat the second FIR filter 4144 may be fixed and only the first FIRfilter 4142 is utilized for compensation in practice; or vice versa. Forexample, a delay chain can be used to implement the second FIR filter4144, wherein the delay chain merely performs a signal delay processupon the signal of the Q-path. The delay time of the second FIR filter4144 is designed to equal the delay time of the first FIR filter 4142,to make sure the delay time of the signals on both paths are equivalentto each other.

The tap coefficient adjustment of the first FIR filter 4142 and thesecond FIR filter 4144 are described in the following paragraphs. FIG. 5is a diagram illustrating the calibration apparatus of FIG. 4 in anotherconfiguration. Specifically, the switching unit 408 is switched to turnon another path as shown in FIG. 5, which is a special setting forcomputing results of the low-pass filter calibration coefficient unit410 corresponding to different low-pass filter calibration testfrequencies; the tap coefficients of the first FIR filter 4142 and thesecond FIR filter 4144 can then be derived in a reverse manner.According to FIG. 5, the signal which passes through the I-path can nowpass the low-pass filter coefficient unit 410 by the switching unit 408.The low-pass filter coefficient unit 410 includes a first low-passfilter calibration coefficient W and a second low-pass filtercalibration coefficient Z. The first low-pass filter calibrationcoefficient W is coupled to the I-path of the transmission terminal 440,for calibrating the amplitude mismatch between the signals of the I-pathand the Q-path induced by the mismatch between the first low-pass filter420 of the I-path of the transmission terminal 440 and the secondlow-pass filter 422 of the Q-path of the transmission terminal 440. Thesecond low-pass filter calibration coefficient Z is coupled between theI-path and the Q-path of the transmission terminal 440, for calibratingthe phase mismatch between the signals of the I-path and the Q-pathinduced by the mismatch between the first low-pass filter 420 of theI-path of the transmission terminal 440 and the second low-pass filter422 of the Q-path of the transmission terminal 440. This is forillustrative purposes only, and not a limitation of the presentinvention. Details of the adjustment of the first low-pass filtercalibration coefficient W and the second low-pass filter calibrationcoefficient Z may be designed according to practical considerations,such as accuracy and cost requirements. Moreover, the first low-passfilter calibration coefficient W and the second low-pass filtercalibration coefficient Z are interchangeable.

The low-pass filter test signal generating unit 404 transmits N low-passfilter test signals TSL₁˜TSL_(N), wherein N can be any number greaterthan 0. The low-pass filter test signals TSL₁˜TSL_(N) go through themixer calibration coefficient unit 406, the switching unit 408, thelow-pass filter coefficient unit 410, and then go through the FIRfiltering unit 414 with the initial setting and the transmissionterminal 440, and loop back to the receiving terminal 432. A spectrumanalysis is performed upon the received signal by the spectrum analysisunit 434 to obtain a plurality of low-pass filter spectrum analysisresults. The low-pass filter spectrum analysis results at least indicateinformation associated with a plurality of image signals correspondingto the low-pass filter test signals TSL₁˜TSL_(N). It should be notedthat the low-pass filter test signals TSL₁˜TSL_(N) are single tonesignals having low-pass filter calibration test frequenciesf_(tsl1)˜f_(tslN), respectively. Since only the mismatches occurring atthe normal mode of the transmitter 400 are under consideration, thelow-pass filter calibration test frequencies f_(tsl1)˜f_(tslN) may bewithin the target bandwidth of the normal node of the transmitter 400.The number and distribution of the low-pass filter calibration testfrequencies f_(tsl1)˜f_(tslN) can directly influence the calibrationaccuracy of the first FIR filter 4142 and the second FIR filter 4144.The tap number and the allocation of the low-pass filter calibrationtest frequencies f _(tsl1)˜f_(tslN) of the first FIR filter 4142 and thesecond FIR filter 4144 should be designed based on comprehensiveconsiderations regarding cost and accuracy desired.

For each of the low-pass filter test signals TSL₁˜TSL_(N), the low-passfilter calibration coefficient adjustment unit 438 can adjust the firstlow-pass filter calibration coefficient W to reduce the image signaltoward a relative minimum value. The corresponding first low-pass filtercalibration coefficient W is preserved as first low-pass filter resultsW₁˜W_(N); and then the low-pass filter calibration coefficientadjustment unit 438 can adjust the second low-pass filter calibrationcoefficient Z to reduce the image signal toward a relative minimumvalue. The corresponding second low-pass filter calibration coefficientZ is preserved as second low-pass filter results Z₁˜Z_(N). After thefirst low-pass filter results W₁˜W_(N) and the second low-pass filterresults Z₁˜Z_(N) are completely derived, the tap coefficient computingunit 412 can therefore derive the tap coefficients of the first FIRfilter 4142 and the second FIR filter 4144. Details are given in thefollowing paragraphs.

A Q-path frequency response computing unit 4122 of the tap coefficientcomputing unit 412 performs a Fourier transform upon the second FIRfilter 4144 of the Q-path. In practice, it is feasible to perform anN-point fast Fourier transform (FFT) upon the second FIR filter 4144 atthe low-pass filter calibration test frequencies f_(tsl1)˜f_(tslN),respectively, to obtain a plurality of frequency responses B₁˜B_(N)corresponding to the low-pass filter calibration test frequenciesf_(tsl1)˜f_(tslN). Equation (3) below is based on equation (1) and (2),and the concept of equation (3) is to derive the I-path frequencyresponses A₁˜A_(N) according to the plurality of frequency responsesB₁˜B_(N), the first low-pass filter results W₁˜W_(N) and the secondlow-pass filter results Z₁˜Z_(N) corresponding to the low-pass filtercalibration test frequencies f_(tsl1)˜f_(tslN).

$\begin{matrix}\begin{matrix}{A_{i} = {B_{i} \times \frac{1}{R_{i}} \times {\exp \left( {- {j\Phi}} \right)}}} \\{= {B_{i} \times W_{i} \times {\cos \left( {- {\arctan \left( Z_{i} \right)}} \right)} \times {\exp \left( {j\; {\arctan \left( Z_{i} \right)}} \right)}}}\end{matrix} & (3)\end{matrix}$

where i=1˜N.

FIG. 6 is a diagram illustrating the first I-path frequency responsecomputing unit according to an embodiment of the present invention.Please note that the first I-path frequency response computing unit 4124shown in FIG. 6 is based on equation (3). In practice, equation (3) canbe further simplified as equation (4) below by approximation.

$\begin{matrix}\begin{matrix}{A_{i} = {B_{i} \times W_{i} \times {\cos \left( {- {\arctan \left( Z_{i} \right)}} \right)} \times {\exp \left( {j\; {\arctan \left( Z_{i\;} \right)}} \right)}}} \\{\sim{= {B_{i} \times W_{i} \times {\cos \left( Z_{i} \right)} \times \left( {{\cos \left( Z_{i} \right)} + {{jsin}\left( Z_{i} \right)}} \right)}}} \\{{\sim{= {B_{i} \times W_{i} \times \left( {1 - \frac{Z_{i}^{2}}{2}} \right)\left( {\left( {1 - \frac{Z_{i}^{2}}{2}} \right) + {j\; Z_{i}}} \right)}}},}\end{matrix} & (4)\end{matrix}$

where i=1˜N.

FIG. 7 is a diagram illustrating the first I-path frequency responsecomputing unit according to another embodiment of the present invention.Please note that the first I-path frequency response computing unit 4124shown in FIG. 7 is based on equation (4).

A coefficient computing unit 4126 of the tap coefficient computing unit412 performs the inverse Fourier transform upon the I-path frequencyresponse A₁˜A_(N), and a real part of the inverse transform result isused as the tap coefficients of the first FIR filter 4142. In practice,it is feasible to perform an inverse fast Fourier transform (iFFT) uponthe I-path frequency response A₁˜A_(N), respectively, to obtain the tapcoefficients of the first FIR filter 4142.

According to the above deductions, the final result of the FIR filteringunit 414 is the first FIR filter 4142, wherein the tap coefficients arederived as above; and the second FIR filter 4144 is the delay chainwherein the delay time is the same as that of the first FIR filter 4142.At this point, all the essential calibration parameters of thetransmission terminal 440 of this embodiment are ready. The transmitter400 can perform the normal data transmission and reception by switchingthe switching unit 408 back to the configuration of FIG. 4. Thedifference is that the performance of the transmitter 440 can beimproved with the help of the mixer calibration coefficient unit 406 andthe FIR filtering unit 414.

FIG. 8 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to another embodiment of the presentinvention; wherein one of the first signal path and the second signalpath is an I-path; and the other is a Q-path. The difference between thetransmitter 800 of FIG. 8 and the transmitter 400 of FIG. 4 is that asecond I-path frequency response computing unit 8124 of a tapcoefficient computing unit 812 of the transmitter 800 can replace theQ-path frequency response computing unit 4122 and the first I-pathfrequency response computing unit 4124. In addition, a switching unit805 is located before the mixer calibration coefficient unit 406. Pleasenote that the configuration of FIG. 8 is for deriving the firstcoefficient X and the second coefficient Y, wherein the switching modeof the switching unit 805 and the switching mode of the switching unit408 are presented. In other words, a test signal generated by the mixertest signal generating unit 402 passes the mixer calibration coefficientunit 406, but does not pass the low-pass filter calibration coefficientunit 410. FIG. 9 is a diagram illustrating the calibration apparatus ofFIG. 8 in another configuration. Specifically, both the switching unit805 and the switching unit 408 are switched to turn on another path asshown in FIG. 8, i.e. the test signal generated by the mixer test signalgenerating unit 402 does not pass the mixer calibration coefficient unit406, but does pass the low-pass filter calibration coefficient unit 410.Related descriptions regarding the rest of the operations can be foundin previous paragraphs and are therefore omitted here for brevity. Asfor the tap coefficient computing unit 812, compared with the tapcoefficient computing unit 412, the I-path frequency responses A₁˜A_(N)can be directly derived by the tap coefficient computing unit 812according to the first low-pass filter results W₁˜W_(N), the secondlow-pass filter results Z₁˜Z_(N) corresponding to the low-pass filtercalibration test frequencies f_(tsl1)˜f_(tslN), the first mixercalibration coefficient X and the second mixer calibration coefficientY.

$\begin{matrix}\begin{matrix}{A_{i} = {\frac{W_{i}}{1 + Z_{i}}\left( {1 + {j\; Y}} \right)\left( {1 - {j\; Z_{i}}} \right)X^{- 1}}} \\{= {{\cos^{2}\left( {\arctan \left( Z_{i} \right)} \right)}{W_{i}\left( {1 + {j\; Y}} \right)}\left( {1 - {j\; Z_{i}}} \right)X^{- 1}}}\end{matrix} & (5)\end{matrix}$

where i=1˜N.

FIG. 10 is a diagram illustrating the second I-path frequency responsecomputing unit according to an embodiment of the present invention. Itshould be noted that the second I-path frequency response computing unit8124 shown in FIG. 10 is based on equation (5). In practice, equation(5) can be further simplified as equation (6) below by utilizing theTaylor series to expand cos²(arc tan(Z_(i))) to (1−Z_(i) ²+Z_(i) ⁴+ . .. ), wherein the first terms are preserved.

$\begin{matrix}\begin{matrix}{A_{i} = {{\cos^{2}\left( {\arctan \left( Z_{i} \right)} \right)}{W_{i}\left( {1 + {j\; Y}} \right)}\left( {1 - {j\; Z_{i}}} \right)X^{- 1}}} \\{\approx {\left( {1 - \frac{Z_{i}^{2}}{2} + {\frac{3}{8}W_{i}^{4}}} \right)^{2}{W_{i}\left( {1 + {j\; Y}} \right)}\left( {1 - {j\; Z_{i}}} \right)X^{- 1}}} \\{\approx {\left( {1 - Z_{i}^{2} + Z_{i}^{4}} \right)\left( {1 + {j\; Y}} \right)\left( {1 - {j\; Z_{i}}} \right)}} \\{= {W_{i}{X^{- 1}\left( {1 - Z_{i}^{2} + Z_{i}^{4}} \right)}\left( {1 + {YZ}_{i} + {j\left( {Y - Z_{i}} \right)}} \right)}}\end{matrix} & (6)\end{matrix}$

FIG. 11 is a diagram illustrating the second I-path frequency responsecomputing unit according to another embodiment of the present invention.It should be noted that the second I-path frequency response computingunit 8124 shown in FIG. 11 is based on equation (6).

FIG. 12 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to an embodiment of the presentinvention; wherein one of the first signal path and the second signalpath is an I-path; and the other is a Q-path. Provided thatsubstantially the same result is achieved, the steps in FIG. 12 need notbe in the exact order shown and need not be contiguous; that is, othersteps can be intermediate. Some steps in FIG. 12 may be omittedaccording to various embodiments or requirements. The calibration methodshown in FIG. 12 can be applied to the transmitter 400 shown in FIG. 4and FIG. 5. Details of the calibration method are described as follows.

Step 1202: additionally configuring at least one mixer calibrationcoefficient at a transmission terminal of the transmitter;

Step 1204: producing a first transmission signal according to at leastone mixer test signal and the mixer calibration coefficient, and loopingback the first transmission signal for spectrum analysis to derive atleast one mixer spectrum analysis result;

Step 1206: adjusting the mixer calibration coefficient according to themixer spectrum analysis result to derive a final value of the mixercalibration coefficient for calibrating a mismatch between a first mixerof the first signal path and a second mixer of the second signal path;

Step 1208: additionally configuring at least one filter calibrationcoefficient at a transmission terminal of the transmitter;

Step 1210: generating a second transmission signal according to at leastone filter test signal and the filter calibration coefficient, andlooping back the second transmission signal to perform spectrum analysisfor deriving at least one filter spectrum analysis result;

Step 1212: adjusting the filter calibration coefficient of thetransmission terminal according to the filter spectrum analysis result;

Step 1214: utilizing a delay chain to act as the second signal path FIRfilter, wherein the delay chain performs a signal delay process upon thesecond signal path, and a delay time of the signal delay processcorresponds to a delay time of the first signal path FIR filteringprocess of the first signal path FIR filter;

Step 1216: deriving at least one second signal path frequency responseof the second signal path FIR filter at the filter calibration testfrequency;

Step 1218: obtaining at least one first signal path frequency responseaccording to the second signal path frequency response, the first filtercalibration coefficient result and the second filter calibrationcoefficient result corresponding to the filter calibration testfrequency;

Step 1220: deriving the tap coefficient of the first signal path FIRfilter according to the first signal path frequency response; and

Step 1222: performing the first signal path FIR filtering process uponthe first signal path by allowing the first signal path FIR filter to bepassed and the filter calibration coefficient to not be passed, tocalibrate the mismatch between the first filter of the first signal pathand the second filter of the second signal path.

Those skilled in the art will readily understand the calibration methodshown in FIG. 12 after reading the above paragraphs regarding thetransmitter 400 shown in FIG. 4 and FIG. 5. Further description istherefore omitted here for brevity.

FIG. 13 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a transmitter according to another embodiment of the presentinvention; wherein one of the first signal path and the second signalpath is an I-path; and the other is a Q-path. Provided thatsubstantially the same result is achieved, the steps in FIG. 13 need notbe in the exact order shown and need not be contiguous; that is, othersteps can be intermediate. Some steps in FIG. 13 may be omittedaccording to various embodiments or requirements. The calibration methodshown in FIG. 13 can be applied to the transmitter 800 shown in FIG. 8and FIG. 9. Details of the calibration method are described as follows.

Step 1202: additionally configuring at least one mixer calibrationcoefficient at a transmission terminal of the transmitter;

Step 1204: producing a first transmission signal according to at leastone mixer test signal and the mixer calibration coefficient, and loopingback the first transmission signal for spectrum analysis to derive atleast one mixer spectrum analysis result;

Step 1206: adjusting the mixer calibration coefficient according to themixer spectrum analysis result to derive a final value of the mixercalibration coefficient for calibrating a mismatch between a first mixerof the first signal path and a second mixer of the second signal path;

Step 1208: additionally configuring at least one filter calibrationcoefficient at a transmission terminal of the transmitter;

Step 1310: generating the second transmission signal by controlling thefilter test signal to start from the transmission terminal and to passthrough the filter calibration coefficient but not passing the mixercalibration coefficient, and looping back the second transmission signalto perform spectrum analysis for deriving at least one filter spectrumanalysis result;

Step 1212: adjusting the filter calibration coefficient of thetransmission terminal according to the filter spectrum analysis result;

Step 1214: utilizing a delay chain to act as the second signal path FIRfilter, wherein the delay chain performs a signal delay process upon thesecond signal path, and a delay time of the signal delay processcorresponds to a delay time of the first signal path FIR filteringprocess of the first signal path FIR filter;

Step 1316: deriving at least one first signal path frequency responseaccording to at least one first filter result, at least one the secondfilter result and the mixer calibration coefficient;

Step 1318: deriving the tap coefficient of the first signal path FIRfilter according to the first signal path frequency response; and

Step 1222: performing the first signal path FIR filtering process uponthe first signal path by allowing the first signal path FIR filter to bepassed and the filter calibration coefficient to not be passed, tocalibrate the mismatch between the first filter of the first signal pathand the second filter of the second signal path.

Those skilled in the art will readily understand the calibration methodshown in FIG. 13 after reading the above paragraphs regarding thetransmitter 800 shown in FIG. 8 and FIG. 9. Further description istherefore omitted here for brevity.

FIG. 14 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention;wherein one of the first signal path and the second signal path is anI-path; and the other is a Q-path. The receiver 1400 includes at leastone portion (e.g. a portion or all) of an electronic device, wherein theelectronic device includes at least a transmission circuit and areceiving circuit. For example, the receiver 1400 may comprise a portionof an electronic device, and more particularly, the electronic deviceincludes at least a transmission circuit and at least a receivingcircuit. In another example, the receiver 1400 can be the whole of theelectronic device mentioned above. Examples of the electronic device mayinclude, but are not limited to, a mobile phone (e.g. a multifunctionalmobile phone), a mobile computer (e.g. tablet computer), a personaldigital assistant (PDA), and a personal computer such as a laptopcomputer. For example, the receiver 1400 may be a process module of theelectronic device, such as a processor. In another example, the receiver1400 may be the entire electronic device; however, this is forillustrative purposes, and not a limitation of the present invention.According to an alternative design of the present invention, thereceiver 1400 is a system of the electronic device, and the electronicdevice is a sub-system of the system. More particularly, the electronicdevice may include an OFDM circuit, wherein the receiver 1400 is able tocalibrate the OFDM circuit, although this is not a limitation of thepresent invention.

As shown in FIG. 14, the receiver 1400 includes a mixer test signalgenerating unit 1402, a low-pass filter test signal generating unit1404, a mixer calibration coefficient unit 1406, a switching unit 1408,a low-pass filter calibration coefficient unit 1410, a tap coefficientcomputing unit 1412, an FIR filtering unit 1414, a firstanalog-to-digital converter (ADC) 1416, a second ADC 1418, a firstlow-pass filter 1420, a second low-pass filter 1422, a first mixer 1424,a second mixer 1426, an oscillator 1428, a low-noise amplifier 1430, atransmission terminal 1432, a spectrum analysis unit 1434, a mixercalibration coefficient adjustment unit 1436 and a low-pass filtercalibration coefficient adjustment unit 1438. According to the disclosedembodiment, each time after the receiver 1400 is activated (e.g. thereceiver 1400 is powered on or reset) and before a normal datatransmission starts, in order to improve mismatches of circuitcharacteristics between an I-path (i.e. the path of the first mixer1424, the first low-pass filter 1420 and the first ADC 1416) and aQ-path (i.e. the path of the second mixer 1426, the second low-passfilter 1422 and the second ADC 1418) of a receiving terminal 1440(including at least the first ADC 1416, the second ADC 1418, the firstlow-pass filter 1420, the second low-pass filter 1422, the first mixer1424, the second mixer 1426, and the oscillator 1428) of the receiver1400, the receiver 1400 enters into a calibration parameters computingmode. To be more specific, at the calibration parameters computing mode,calibration parameters can be optimized through a computing process withrespect to the difference between the I-path and the Q-path of thereceiving terminal 1440 of the receiver 1400. After that, the receivingterminal 1440 is allowed to enter a normal data receiving mode toreceive data by employing the additional calibration parameters derivedby above steps. This is for illustrative purposes, however, and not alimitation of the present invention. For example, the first low-passfilter 1420 and the second low-pass filter 1422 of the receiver 1400 maybe filters of another type.

The principles of the calibration process regarding the first mixer1424, the second mixer 1426, the first low-pass filter 1420, secondlow-pass filter 1422, the first analog-to-digital converter 1416 and thesecond analog-to-digital converter 1418 of the receiving terminal 1440of the receiver 1400 of FIG. 14 are substantially the same as those ofthe first mixer 424, the second mixer 426, the first low-pass filter420, the second low-pass filter 422, the first digital-to-analogconverter 416 and the second digital-to-analog converter 418 of thetransmission terminal 440 of the transmitter 400 of FIG. 4. Thoseskilled in the art will readily understand the details of the operationof the receiver 1400 shown in FIG. 14 after reading the above paragraphsregarding the transmitter 400 shown in FIG. 4 and FIG. 5. Furtherdescription is therefore omitted here for brevity.

FIG. 15 is a diagram illustrating a calibration apparatus applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to another embodiment of the presentinvention; wherein one of the first signal path and the second signalpath is an I-path; and the other is a Q-path. The difference between thereceiver 1400 of FIG. 14 and the receiver 1500 of FIG. 15 is that asecond I-path frequency response computing unit 15124 of a tapcoefficient computing unit 1512 of the receiver 1500 can replace theQ-path frequency response computing unit 14122 and the first I-pathfrequency response computing unit 14124. The principles of thecalibration process regarding the tap coefficient computing unit 1512 ofthe receiving terminal 1440 of the receiver 1500 of FIG. 15 aresubstantially the same as those of the tap coefficient computing unit812 of the transmitter 800 of FIG. 8. Those skilled in the art willreadily understand the details of the operation of the second I-pathfrequency response computing unit 15124 shown in FIG. 15 after readingthe above paragraphs regarding FIG. 8 and FIG. 10˜FIG. 11. Furtherdescription is therefore omitted here for brevity.

FIG. 16 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention;wherein one of the first signal path and the second signal path is anI-path; and the other is a Q-path. Provided that substantially the sameresult is achieved, the steps in FIG. 16 need not be in the exact ordershown and need not be contiguous; that is, other steps can beintermediate. Some steps in FIG. 16 maybe omitted according to variousembodiments or requirements. The calibration method shown in FIG. 16 canbe applied to the receiver 1400 shown in FIG. 14. Details of thecalibration method are described as follows.

Step 1602: additionally configuring at least one mixer calibrationcoefficient at a receiving terminal of the receiver;

Step 1604: outputting the mixer test signal at a transmission terminalof the receiver as a first transmission signal, and looping back thefirst transmission signal and performing spectrum analysis upon thereceived first transmission signal after it passes through the mixercalibration coefficient, for deriving at least one mixer spectrumanalysis result;

Step 1606: adjusting the mixer calibration coefficient of the receiveraccording to the mixer spectrum analysis result to derive a final valueof the mixer calibration coefficient for calibrating a mismatch betweena first mixer of the first signal path and a second mixer of the secondsignal path;

Step 1608: besides the mixer calibration coefficient, additionallyconfiguring at least one filter calibration coefficient at the receivingterminal of the receiver;

Step 1610: outputting the filter test signal at a transmission terminalof the receiver as a second transmission signal, and looping back thesecond transmission signal and performing spectrum analysis upon thereceived second transmission signal after it passes through the filtercalibration coefficient and the mixer calibration coefficient of thereceiving terminal, for deriving at least one filter spectrum analysisresult;

Step 1612: adjusting the filter calibration coefficient of the receivingterminal according to the filter spectrum analysis result;

Step 1614: utilizing a delay chain to act as the second signal path FIRfilter, wherein the delay chain performs a signal delay process upon thesecond signal path, and a delay time of the signal delay processcorresponds to a delay time of the first signal path FIR filteringprocess of the first signal path FIR filter;

Step 1616: deriving at least one second signal path frequency responseof the second signal path FIR filter at the filter calibration testfrequency;

Step 1618: obtaining at least one first signal path frequency responseaccording to the second signal path frequency response, the first filtercalibration coefficient result and the second filter calibrationcoefficient result corresponding to the filter calibration testfrequency;

Step 1620: deriving the tap coefficient of the first signal path FIRfilter according to the first signal path frequency response; and

Step 1622: performing the first signal path FIR filtering process uponthe first signal path by allowing the first signal path FIR filter to bepassed and the filter calibration coefficient to not be passed, in orderto calibrate the mismatch between the first filter of the first signalpath and the second filter of the second signal path.

Those skilled in the art will readily understand the calibration methodshown in FIG. 16 after reading the above paragraphs regarding thetransmitter 1400 shown in FIG. 14. Further description is thereforeomitted here for brevity.

FIG. 17 is a flowchart illustrating a calibration method applied forcalibrating mismatches between a first signal path and a second signalpath of a receiver according to an embodiment of the present invention;wherein one of the first signal path and the second signal path is anI-path; and the other is a Q-path. Provided that substantially the sameresult is achieved, the steps in FIG. 17 need not be in the exact ordershown and need not be contiguous; that is, other steps can beintermediate. Some steps in FIG. 17 may be omitted according to variousembodiments or requirements. The calibration method shown in FIG. 17 canbe applied to the receiver 1500 shown in FIG. 15. Details of thecalibration method are described as follows.

Step 1602: additionally configuring at least one mixer calibrationcoefficient at a receiving terminal of the receiver;

Step 1604: outputting the mixer test signal at a transmission terminalof the receiver as a first transmission signal, and looping back thefirst transmission signal and performing spectrum analysis upon thereceived first transmission signal after it passes through the mixercalibration coefficient, for deriving at least one mixer spectrumanalysis result;

Step 1606: adjusting the mixer calibration coefficient of the receiveraccording to the mixer spectrum analysis result to derive a final valueof the mixer calibration coefficient for calibrating a mismatch betweena first mixer of the first signal path and a second mixer of the secondsignal path;

Step 1608: besides the mixer calibration coefficient, additionallyconfiguring at least one filter calibration coefficient at the receivingterminal of the receiver;

Step 1710: outputting the filter test signal at a transmission terminalof the receiver as a second transmission signal, and looping back thesecond transmission signal and performing spectrum analysis upon thereceived second transmission signal after it passes through the filtercalibration coefficient of the receiving terminal, for deriving at leastone filter spectrum analysis result;

Step 1612: adjusting the filter calibration coefficient of the receivingterminal according to the filter spectrum analysis result;

Step 1614: utilizing a delay chain to act as the second signal path FIRfilter, wherein the delay chain performs a signal delay process upon thesecond signal path, and a delay time of the signal delay processcorresponds to a delay time of the first signal path FIR filteringprocess of the first signal path FIR filter;

Step 1716: deriving at least one first signal path frequency responseaccording to at least one first filter result, at least one the secondfilter result and the mixer calibration coefficient;

Step 1718: deriving the tap coefficient of the first signal path FIRfilter according to the first signal path frequency response;

Step 1622: performing the first signal path FIR filtering process uponthe first signal path by allowing the first signal path FIR filter to bepassed and the filter calibration coefficient to not be passed, in orderto calibrate the mismatch between the first filter of the first signalpath and the second filter of the second signal path.

Those skilled in the art will readily understand the calibration methodshown in FIG. 17 after reading the above paragraphs regarding thetransmitter 1500 shown in FIG. 15. Further description is thereforeomitted here for brevity.

The main purpose of the present invention is to compensate mismatchesbetween an I-path and a Q-path of a transmitter/receiver through theabove methods and apparatus, and especially to compensate mismatchesbetween a mixer of the I-path and a mixer of the Q-path of atransmitter/receiver and to compensate mismatches between a low-passfilter of the I-path and a low-pass filter of the Q-path of thetransmitter/receiver, which improves the performance of electronicdevices.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for calibrating mismatches between afirst signal path and a second signal path of a transmitter, wherein oneof the first signal path and the second signal path is an in-phasesignal path; and the other is a quadrature signal path, and the methodcomprises: additionally configuring at least one mixer calibrationcoefficient at a transmission terminal of the transmitter; producing afirst transmission signal according to at least one mixer test signaland the mixer calibration coefficient, and looping back the firsttransmission signal for spectrum analysis to derive at least one mixerspectrum analysis result; adjusting the mixer calibration coefficientaccording to the mixer spectrum analysis result to derive a final valueof the mixer calibration coefficient for calibrating a mismatch betweena first mixer of the first signal path and a second mixer of the secondsignal path; and performing a first signal path finite impulse response(FIR) filtering process upon the first signal path by additionallyutilizing a first signal path FIR filter, and performing a second signalpath FIR filtering process upon the second signal path by additionallyutilizing a second signal path FIR filter, to calibrate a mismatchbetween a first filter of the first signal path and a second filter ofthe second signal path.
 2. The method of claim 1, wherein the mixercalibration coefficient includes at least one first mixer calibrationcoefficient and a second mixer calibration coefficient, and the firstmixer calibration coefficient is used to calibrate amplitude mismatchesbetween the first signal path and the second signal path; and the secondmixer calibration coefficient is used to calibrate phase mismatchesbetween the first signal path and the second signal path.
 3. The methodof claim 2, wherein the mixer test signal includes a first mixercalibration test signal and a second mixer calibration test signal, andthe first mixer calibration test signal has a first mixer calibrationtest frequency and the second mixer calibration test signal has a secondmixer calibration test frequency; and the first mixer calibration testfrequency is formed by adding frequency of a local oscillator of thetransmitter with a specific frequency, and the second mixer calibrationtest frequency is formed by subtracting the specific frequency from thefrequency of the local oscillator of the transmitter.
 4. The method ofclaim 3, wherein the step of adjusting the mixer calibration coefficientaccording to the mixer spectrum analysis result to derive the finalvalue of the mixer calibration coefficient comprises: adjusting thefirst mixer calibration coefficient, and applying the first mixercalibration coefficient which relatively minimizes an image signal ofthe first mixer calibration test signal to be a first result; adjustingthe second mixer calibration coefficient, and applying the second mixercalibration coefficient which relatively minimizes the image signal ofthe first mixer calibration test signal to be a second result; adjustingthe first mixer calibration coefficient, and applying the first mixercalibration coefficient which relatively minimizes an image signal ofthe second mixer calibration test signal to be a third result; adjustingthe second mixer calibration coefficient, and applying the second mixercalibration coefficient which relatively minimizes the image signal ofthe second mixer calibration test signal to be a fourth result; andderiving the final value of the first mixer calibration coefficientaccording to the first result and the third result, and deriving thefinal value of the second mixer calibration coefficient according to thesecond result and the fourth result.
 5. The method of claim 1, whereinthe step of performing the first signal path FIR filtering process uponthe first signal path by additionally utilizing the first signal pathFIR filter comprises: configuring at least one filter calibrationcoefficient at the transmission terminal of the transmitter; generatinga second transmission signal according to at least one filter testsignal and the filter calibration coefficient, and looping back thesecond transmission signal to perform spectrum analysis for deriving atleast one filter spectrum analysis result; adjusting the filtercalibration coefficient of the transmission terminal according to thefilter spectrum analysis result; deriving at least one tap coefficientof the first signal path FIR filter of the transmission terminalaccording to the adjusted filter calibration coefficient; and performingthe first signal path FIR filtering process upon the first signal pathby allowing the first signal path FIR filter to be passed and the filtercalibration coefficient to not be passed, to calibrate the mismatchbetween the first filter of the first signal path and the second filterof the second signal path.
 6. The method of claim 5, wherein the step ofgenerating the second transmission signal according to the filter testsignal and the filter calibration coefficient comprises: generating thesecond transmission signal by controlling the filter calibrationcoefficient to start from the transmission terminal and to pass throughthe mixer calibration coefficient and the filter calibrationcoefficient.
 7. The method of claim 6, wherein the filter calibrationcoefficient at least includes a first filter calibration coefficient anda second filter calibration coefficient; and the first filtercalibration coefficient is used to calibrate amplitude mismatchesbetween the first signal path and the second signal path; and the secondfilter calibration coefficient is used to calibrate phase mismatchesbetween the first signal path and the second signal path.
 8. The methodof claim 7, wherein the filter test signal has at least one filtercalibration test frequency, and the filter calibration test frequency iswithin a target bandwidth of the transmitter.
 9. The method of claim 8,wherein the step of adjusting the filter calibration coefficient of thetransmission terminal according to the filter spectrum analysis resultcomprises: adjusting the first filter calibration coefficient, andapplying the first filter calibration coefficient which relativelyminimizes an image signal of the filter test signal to be at least onefirst filter calibration coefficient result; and adjusting the secondfilter calibration coefficient, and applying the second filtercalibration coefficient which relatively minimizes the image signal ofthe filter test signal to be at least one second filter calibrationcoefficient result.
 10. The method of claim 9, wherein the step ofderiving the tap coefficient of the first signal path FIR filter of thetransmission terminal according to the adjusted filter calibrationcoefficient comprises: deriving at least one second signal pathfrequency response of the second signal path FIR filter at the filtercalibration test frequency; obtaining at least one first signal pathfrequency response according to the second signal path frequencyresponse, the first filter calibration coefficient result and the secondfilter calibration coefficient result corresponding to the filtercalibration test frequency; and deriving the tap coefficient of thefirst signal path FIR filter according to the first signal pathfrequency response.
 11. The method of claim 5, wherein the step ofgenerating the second transmission signal by controlling the filtercalibration coefficient to start from the transmission terminal and topass through the mixer calibration coefficient and the filtercalibration coefficient comprises: generating the second transmissionsignal by controlling the filter test signal to start from thetransmission terminal and to pass through the filter calibrationcoefficient but to not pass through the mixer calibration coefficient.12. The method of claim 11, wherein the filter calibration coefficientat least includes a first filter calibration coefficient and a secondfilter calibration coefficient; and the first filter calibrationcoefficient is used to calibrate amplitude mismatches between the firstsignal path and the second signal path; and the second filtercalibration coefficient is used to calibrate phase mismatches betweenthe first signal path and the second signal path.
 13. The method ofclaim 12, wherein the filter test signal has at least one filtercalibration test frequency, and the filter calibration test frequency iswithin a target bandwidth of the transmitter.
 14. The method of claim13, wherein the step of adjusting the filter calibration coefficient ofthe transmission terminal according to the filter spectrum analysisresult comprises: adjusting the first filter calibration coefficient,and applying the first filter calibration coefficient which relativelyminimizes an image signal of the filter test signal to be at least onefirst filter result; and adjusting the second filter calibrationcoefficient, and applying the second filter calibration coefficientwhich relatively minimizes the image signal of the filter test signal tobe at least one second filter result.
 15. The method of claim 14,wherein the step of deriving the tap coefficient of the first signalpath FIR filter of the transmission terminal according to the adjustedfilter calibration coefficient comprises: deriving at least one firstsignal path frequency response according to the first filter result, thesecond filter result and the mixer calibration coefficient; and derivingthe tap coefficient of the first signal path FIR filter according to thefirst signal path frequency response.
 16. An apparatus for calibratingmismatches between a first signal path and a second signal path of atransmitter, wherein one of the first signal path and the second signalpath is an in-phase signal path; and the other is a quadrature signalpath, and the apparatus comprises: a mixer calibration coefficient unit,coupled to a transmission terminal of the transmitter, wherein the mixercalibration coefficient unit is configured to have at least one mixercalibration coefficient; a mixer test signal generating unit, arrangedfor producing a first transmission signal by controlling at least onemixer test signal to start from the transmission terminal and to passthrough the mixer calibration coefficient; a spectrum analysis unit,arranged for performing spectrum analysis upon the received firsttransmission signal to derive at least one mixer spectrum analysisresult; a mixer calibration coefficient adjustment unit, arranged foradjusting the mixer calibration coefficient according to the mixerspectrum analysis result to derive a final value of the mixercalibration coefficient for calibrating a mismatch between a first mixerof the first signal path and a second mixer of the second signal path;and a finite impulse response (FIR) filtering unit, coupled to thetransmission terminal of the transmitter, arranged for performing afirst signal path FIR filtering process upon the first signal path byadditionally utilizing a first signal path FIR filter, and performing asecond signal path FIR filtering process upon the second signal path byadditionally utilizing a second signal path FIR filter, to calibrating amismatch between a first filter of the first signal path and a secondfilter of the second signal path.
 17. The apparatus of claim 16, whereinthe mixer calibration coefficient includes at least one first mixercalibration coefficient and a second mixer calibration coefficient, andthe first mixer calibration coefficient is used to calibrate amplitudemismatches between the first signal path and the second signal path; andthe second mixer calibration coefficient is used to calibrate phasemismatches between the first signal path and the second signal path. 18.The apparatus of claim 17, wherein the mixer test signal includes afirst mixer calibration test signal and a second mixer calibration testsignal, and the first mixer calibration test signal has a first mixercalibration test frequency and the second mixer calibration test signalhas a second mixer calibration test frequency; and the first mixercalibration test frequency is formed by adding frequency of a localoscillator of the transmitter with a specific frequency, and the secondmixer calibration test frequency is formed by subtracting the specificfrequency from the frequency of the local oscillator of the transmitter.19. The apparatus of claim 18, wherein the mixer calibration coefficientadjustment unit adjusts the first mixer calibration coefficient, andapplies the first mixer calibration coefficient which relativelyminimizes an image signal of the first mixer calibration test signal tobe a first result; adjusts the second mixer calibration coefficient, andapplies the second mixer calibration coefficient which relativelyminimizes the image signal of the first mixer calibration test signal tobe a second result; adjusts the first mixer calibration coefficient, andapplies the first mixer calibration coefficient which relativelyminimizes an image signal of the second mixer calibration test signal tobe a third result; adjusts the second mixer calibration coefficient, andapplies the second mixer calibration coefficient which relativelyminimizes the image signal of the second mixer calibration test signalto be a fourth result; and derives the final value of the first mixercalibration coefficient according to the first result and the thirdresult, and derives the final value of the second mixer calibrationcoefficient according to the second result and the fourth result. 20.The apparatus of claim 16, wherein the spectrum analysis unit furtherperforms spectrum analysis upon the received second transmission signalwhich passes through the filter calibration coefficient of thetransmission terminal, for deriving at least one filter spectrumanalysis result, and the calibration apparatus further comprises: afilter calibration coefficient unit, comprising at least one filtercalibration coefficient; a filter test signal generating unit, arrangedfor outputting at least one filter test signal at the transmissionterminal of the receiver as a second transmission signal; a filtercalibration coefficient adjustment unit, arranged for adjusting thefilter calibration coefficient of the transmission terminal according tothe filter spectrum analysis result; a tap coefficient computing unit,arranged for deriving at least one tap coefficient of the first signalpath FIR filter of the transmission terminal according to the adjustedfilter calibration coefficient; and a switching unit, arranged forperforming the first signal path FIR filtering process upon the firstsignal path by allowing the first signal path FIR filter to be passedand the filter calibration coefficient to not be passed, to calibratethe mismatch between the first filter of the first signal path and thesecond filter of the second signal path.
 21. The apparatus of claim 20,wherein the spectrum analysis unit further performs spectrum analysisupon the received second transmission signal which passes through themixer calibration coefficient and the filter calibration coefficient ofthe transmission terminal, for deriving at least one filter spectrumanalysis result.
 22. The apparatus of claim 21, wherein the filtercalibration coefficient at least includes a first filter calibrationcoefficient and a second filter calibration coefficient; and the firstfilter calibration coefficient is used to calibrate amplitude mismatchesbetween the first signal path and the second signal path; and the secondfilter calibration coefficient is used to calibrate phase mismatchesbetween the first signal path and the second signal path.
 23. Theapparatus of claim 22, wherein the filter test signal has at least onefilter calibration test frequency, and the filter calibration testfrequency is within a target bandwidth of the transmitter.
 24. Theapparatus of claim 23, wherein the filter calibration coefficientadjustment unit adjusts the first filter calibration coefficient, andapplies the first filter calibration coefficient which relativelyminimizes an image signal of the at least one filter test signal to beat least one first filter calibration coefficient result; and adjuststhe second filter calibration coefficient, and applies the second filtercalibration coefficient which relatively minimizes the image signal ofthe at least one filter test signal to be at least one second filtercalibration coefficient result.
 25. The apparatus of claim 24, whereinthe tap coefficient computing unit comprises: a second signal pathfrequency response computing unit, arranged for deriving at least onesecond signal path frequency response of the second signal path FIRfilter at the filter calibration test frequency; a main first signalpath frequency response computing unit, arranged for obtaining at leastone first signal path frequency response according to the second signalpath frequency response, the first filter calibration coefficient resultand the second filter calibration coefficient result corresponding tothe filter calibration test frequency; and a coefficient computing unit,arranged for deriving the tap coefficient of the first signal path FIRfilter according to the first signal path frequency response.
 26. Theapparatus of claim 20, wherein the spectrum analysis unit furtherperforms spectrum analysis upon the received second transmission signalwhich passes through the filter calibration coefficient but does notpass through the mixer calibration coefficient of the transmissionterminal, for deriving at least one filter spectrum analysis result. 27.The apparatus of claim 26, wherein the filter calibration coefficient atleast includes a first filter calibration coefficient and a secondfilter calibration coefficient; and the first filter calibrationcoefficient is used to calibrate amplitude mismatches between the firstsignal path and the second signal path; and the second filtercalibration coefficient is used to calibrate phase mismatches betweenthe first signal path and the second signal path.
 28. The apparatus ofclaim 27, wherein the filter test signal has at least one filtercalibration test frequency, and the filter calibration test frequency iswithin a target bandwidth of the transmitter.
 29. The apparatus of claim28, wherein the filter calibration coefficient adjustment unit adjuststhe first filter calibration coefficient, and applies the first filtercalibration coefficient which relatively minimizes an image signal ofthe at least one filter test signal to be at least one first filterresult; and adjusts the second filter calibration coefficient, andapplies the second filter calibration coefficient which relativelyminimizes the image signal of the filter test signal to be at least onesecond filter result.
 30. The apparatus of claim 29, wherein the tapcoefficient computing unit further comprises: an auxiliary first signalpath frequency response computing unit, arranged for deriving at leastone first signal path frequency response according to the first filterresult, the second filter result and the mixer calibration coefficient;and a coefficient computing unit, arranged for deriving the tapcoefficient of the first signal path FIR filter according to the firstsignal path frequency response.